Control device for working vehicle

ABSTRACT

The invention provides a control system for a working vehicle, which can realize higher work performance and better fuel economy in a compatible way. A controller  10  includes table  10   a   , 10   b  and tables  10   e   , 10   f  for deciding maximum pump absorption torques and engine output torques based on an engine revolution speed, and selectors  10   c   , 10   g  for switching over the decided maximum pump absorption torques and engine output torques depending on a work performance mode or a fuel economy mode is selected. A pump absorption torque characteristic for the fuel economy mode is set so as to provide a relative small maximum pump absorption torques TB in a high revolution range, and an engine output characteristic for the fuel economy mode is set so as to provide a relatively small engine output torque in the high revolution range.

TECHNICAL FIELD

The present invention relates to a control system for a working vehicle,such as a wheel loader or a telescopic handler, in which a transmissionis driven by an engine for traveling of the vehicle and a hydraulic pumpis also driven by the engine to operate a working actuator, therebyperforming predetermined work.

BACKGROUND ART

The related art regarding a control system for the above-mentioned typeof working vehicle is disclosed in JP,B 8-6613 and Japanese Patent No.2968558.

The related art disclosed in JP,B 8-6613 is intended for a system inwhich two kinds of engine output characteristics, i.e., an engine outputcharacteristic adapted for work and an engine output characteristicadapted for traveling, are prepared and the engine outputcharacteristics are switched over from one to the other for control ofan engine output in use depending on whether a vehicle is in a workingstate or a traveling state. When the vehicle is in the traveling stateand a torque converter speed ratio is small (low speed), the amount ofinjected fuel is controlled so that a transmission torque will notexceed the torque in the working state, thereby preventing generation ofan excessive torque applied to a torque converter.

According to the related art disclosed in Japanese Patent No. 2968558,when the sum of respective loads of a travel driving unit and anactuator is smaller than an engine output torque, a pump absorptiontorque is increased to ensure work performance. Also, when the load sumis larger than the engine output torque, the pump absorption torque isreduced to ensure a large travel torque for maintaining a large tractiveforce.

Patent Reference 1: JP,B 8-6613

Patent Reference 2: Japanese Patent No. 2968558

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In a working vehicle, such as a wheel loader or a telescopic handler,work requiring a front operating mechanism to be operated whiletraveling (i.e., combined work of travel and front work using the frontoperating mechanism) is performed in many cases. In such combined work,the amount of work performed by the front operating mechanism variesconsiderably depending on the type of work. When the amount of workcarried out by the front operating mechanism is large in the combinedwork of travel and front work using the front operating mechanism, theabsorption torque of a hydraulic pump also becomes large and the sum ofthe absorption torque of the hydraulic pump and the transmission torque(travel torque) exceeds the engine output torque, thus resulting in anoperating state where the engine output is utilized at full capacity. Inthat type of work, therefore, the engine output torque is desirably setto a level as high as possible in order to increase the workperformance. On the other hand, when the amount of work carried out issmall, the absorption torque of the hydraulic pump also becomes smalland the sum of the absorption torque of the hydraulic pump and thetransmission torque (travel torque) is smaller than the engine outputtorque. In that case, therefore, it is desired to reduce the engineoutput torque, if possible, from the viewpoint of improving fueleconomy.

With the related art disclosed in JP,B 8-6613, the engine outputcharacteristic adapted for work and the engine output characteristicadapted for traveling can be switched over from one to the other. Whenthe engine output characteristic adapted for work is selected, theengine output torque is increased and therefore higher work performanceis expected, and when the engine output characteristic adapted fortraveling is selected, the engine output torque is reduced and thereforethe fuel economy effect is expected. However, the disclosed related artis disadvantageous in that, in the work requiring the operation of thefront operating device, the engine output characteristic adapted forwork is selected even when the amount of work carried out is small, andhence the fuel economy effect cannot be obtained.

With the related art disclosed in Japanese Patent No. 2968558, theabsorption torque of the hydraulic pump is changed depending on theworking state, while the engine output characteristic is held constant.Accordingly, the fuel economy effect cannot be obtained in small-loadwork.

Thus, any related art has a difficulty in realizing higher workperformance and better fuel economy in a compatible way.

An object of the present invention is to provide a control system for aworking vehicle, which can realize higher work performance and betterfuel economy in a compatible way.

Means for Solving the Problem

(1) To achieve the above object, the present invention provides acontrol system for a working vehicle comprising an engine, a fuelinjector for controlling an output torque and revolution speed of theengine, a transmission for traveling which is driven by the engine, avariable displacement hydraulic pump driven by the engine, and ahydraulic actuator driven by a hydraulic fluid delivered from thehydraulic pump, and first pump torque control means for controlling anabsorption torque of the hydraulic pump not to exceed a maximumabsorption torque, wherein the control system comprises switching-overmeans; engine torque control means for selecting one of at least twopreset engine output torque characteristics in response to aninstruction from the switching-over means and controlling the fuelinjector in accordance with the selected engine output characteristic,thereby controlling the output torque of the engine; and second pumptorque control means for selecting one of at least two preset pumpabsorption torque characteristics in response to the instruction fromthe switching-over means and controlling the maximum absorption torqueof the hydraulic pump in accordance with the selected pump absorptiontorque characteristic.

Thus, the switching-over means, the engine torque control means, and thesecond pump torque control means are provided, and the engine outputtorque characteristics and the pump absorption torque characteristicsare switched over in response to the instruction from the switching-overmeans to control the fuel injector and the pump torque control means,thereby controlling the engine output torque and the pump absorptiontorque. Accordingly, when the amount of work carried out is large, thework performance can be increased by selecting the engine outputcharacteristic that provides a relatively large engine output torque,and when the amount of work carried out is small, the fuel economyeffect can be obtained by selecting the engine output characteristicthat provides a relatively small engine output torque. As a result,higher work performance and better fuel economy can be realized in acompatible way.

(2) In above (1), preferably, the switching-over means is a switch forinstructing one of a work performance mode and a fuel economy mode; theengine torque control means selects the output torque characteristicproviding, in the fuel economy mode, a slightly smaller engine outputtorque in a relatively high range of the engine revolution speed thanthat in the work performance mode; and the second pump torque controlmeans selects the pump absorption torque characteristic providing, inthe fuel economy mode, a slightly smaller maximum pump absorption torquein the relatively high range of the engine revolution speed than that inthe work performance mode corresponding to a reduction of the engineoutput torque made by the engine torque control means.

In a working vehicle, such as a wheel loader or a telescopic handler, atravel force (tractive force) is important. It is therefore desired thatthe travel force be as large as possible regardless of any workingstate.

In the fuel economy mode, the maximum pump absorption torquecharacteristic is selected which provides a slightly smaller pumpabsorption torque in the relatively high range of the engine revolutionspeed than that in the work performance mode corresponding to areduction of the engine output torque made by the engine torque controlmeans. Even with the engine output torque slightly reduced, therefore,it is possible to avoid a reduction of the travel torque and to obtaingood workability.

(3) In above (1) or (2), preferably, the engine torque control meanscomputes a fuel injection amount corresponding to the engine revolutionspeed at the current time in accordance with the selected engine outputcharacteristic and controls the fuel injector by limiting a target fuelinjection amount to be not larger than the computed fuel injectionamount.

That feature enables the selected engine output characteristic to beobtained as intended.

(4) In above (1) or (2), preferably, the engine torque control meanssets, as the engine output characteristic, a fuel injection amountcharacteristic with respect to the engine revolution speed and controlsthe fuel injector by limiting a target fuel injection amount to be notlarger than a fuel injection amount decided in accordance with the fuelinjection amount characteristic.

That feature enables the selected engine output characteristic to beobtained as intended.

Advantages of the Invention

According to the present invention, it is possible to realize higherwork performance and better fuel economy in a compatible way.

Also, even when the engine output torque is relatively small in the fueleconomy mode, a reduction of the travel torque can be avoided and goodworkability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an overall driving system including acontrol system for a working vehicle according to a first embodiment ofthe present invention.

FIG. 2 shows an external appearance of a wheel loader as one example ofthe working vehicle to which the present invention is applied.

FIG. 3 is a functional block diagram showing details of control executedby a controller in engine control and pump control.

FIG. 4 is a graph comparatively showing an engine output characteristicfor a work performance mode and an engine output characteristic for afuel economy mode, those characteristics being set in a table.

FIG. 5 is a graph showing the relationship between pump pressure andpump tilting when torque control is executed by a torque controlregulator.

FIG. 6 is a functional block diagram showing details of processingexecuted in a fuel injector control unit.

FIG. 7 is a graph showing how a limit value of an upper limiter isincreased and decreased by a limit computing unit with an increase anddecrease of a maximum fuel injection amount.

FIG. 8 is a graph showing the relationships among engine output torque,maximum pump absorption torque, and transmission torque when the workperformance mode is selected.

FIG. 9 is a graph showing the relationships among engine output torque,maximum pump absorption torque, and transmission torque when the fueleconomy mode is selected.

FIG. 10 is a functional block diagram showing details of controlexecuted by a controller in engine control and pump control according toa second embodiment of the present invention.

FIG. 11 is a functional block diagram showing details of processingexecuted in a fuel injector control unit.

REFERENCE NUMERALS

-   -   1 engine    -   2 electronic fuel injector    -   4 torque converter    -   5 transmission    -   6 axle    -   8 travel pedal    -   10 controller    -   10 a, 10 b tables regarding maximum pump absorption torque    -   10 c selector    -   10 d output unit    -   10 e, 10 f tables regarding engine output torque    -   10 g selector    -   10 h fuel injector control unit    -   11 mode select switch    -   15 hydraulic pump    -   16 control valve    -   17 actuator    -   21 torque control regulator    -   22 torque control solenoid valve    -   25 revolution sensor    -   100 a revolution speed deviation computing unit    -   100 b fuel injection amount converting unit    -   100 c integral addition unit    -   100 d maximum fuel injection amount computing unit    -   100 e limit computing unit    -   100 f primary delay element

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

FIG. 1 is a block diagram of an overall driving system including acontrol system for a working vehicle according to a first embodiment ofthe present invention.

In FIG. 1, a working vehicle according to this embodiment includes adiesel engine (hereinafter referred to simply as an “engine” 1) servingas a prime mover. The engine 1 is provided with an electronic fuelinjector 2, and the electronic fuel injector 2 controls the outputtorque and revolution speed of the engine 1. A transmission 5 fortraveling, including a torque converter 4, is coupled to an output shaftof the engine 1. The engine 1 drives the transmission 5, whereupon axles6 are rotated so that the vehicle travels. A travel pedal 8 is providedas means for instructing a target revolution speed of the engine 1. Asignal from the travel pedal 8 is inputted to a controller 10. Inaccordance with the input signal, the controller 10 outputs a controlsignal to the electronic fuel injector 2 and controls the fuel injectionamount. Further, a mode select switch 11 is provided as means forinstructing switching-over between a work performance mode and a fueleconomy mode, and a signal from the mode select switch 11 is alsoinputted to the controller 10.

A variable displacement hydraulic pump 15 is coupled to the output shaftof the engine 1, and the hydraulic pump 15 is driven by the engine 1 todeliver a hydraulic fluid. A control valve 16 is connected to a fluiddelivery line of the hydraulic pump 15. The control valve 16 is operatedby operating means, such as a control lever, for supply of the hydraulicfluid to an actuator 17. The actuator 17 is, e.g., a hydraulic cylinderfor driving a front operating mechanism of the wheel loader.

The hydraulic pump 15 is provided with a torque control regulator 21.When the delivery pressure of the hydraulic pump 15 rises, the torquecontrol regulator 21 reduces the tilting (displacement) of the hydraulicpump 15 in a responsive manner to control the tilting (displacement) ofthe hydraulic pump 15 so that the absorption torque of the hydraulicpump 15 will not exceed a setting value (maximum pump absorptiontorque). The setting value (maximum pump absorption torque) of thetorque control regulator 21 is variable and controlled by a torquecontrol solenoid valve 22. The torque control solenoid valve 22 is asolenoid proportional valve operated with the delivery pressure of thehydraulic pump 15 serving as a hydraulic pressure source, and isoperated by a control signal outputted from the controller 10.

Further, the engine 1 is provided with a revolution sensor 25 fordetecting the engine revolution speed, and a signal from the revolutionsensor 25 is also inputted to the controller 10.

FIG. 2 shows an external appearance of a wheel loader as one example ofthe working vehicle to which the present invention is applied. In FIG.2, numeral 100 denotes the wheel loader. The wheel loader 100 comprisesa front body section 101 and a rear body section 102. The front bodysection 101 and the rear body section 102 are coupled to each otherthrough a coupler 103 in an articulately flexible way. A front operatingmechanism 105 and wheels (front wheels) 106 are mounted to the frontbody section 101, while a cab 107 and wheels (rear wheels) 108 aremounted to the rear body section 102. An operator's seat 110, a steeringwheel 111, and a control lever 112 are provided in the cab 107. Thefront operating mechanism 105 is made up of a bucket 120 and a lift arm121. The bucket 120 performs the tilting/dumping operation withcontraction/extension of a bucket cylinder 122, and the lift arm 121 isoperated upward and downward with extension/contraction of an armcylinder 123. The actuator 17 shown in FIG. 1 is representative of thebucket cylinder 122 and the arm cylinder 123.

Further, the engine 1 and the hydraulic pump 15, shown in FIG. 1, aredisposed in the rear body section 102 along with the control valve 16,the torque control regulator 21 and the torque control valve 22, and therear wheels 108 are driven by the engine 1 through the transmission 5and the axles 6. The travel pedal 8 is disposed on a floor of the cab107, and the mode select switch 11 is disposed on A front cabinet 113 ofthe cab 107. The controller 10 is disposed in an appropriate positionwithin the cab 107, e.g., a position below the operator's seat 110.

The actuator 17 shown in FIG. 1 is representative of the bucket cylinder122 and the arm cylinder 123, and the front operating mechanism 105 canbe operated by driving those cylinders.

FIG. 3 is a functional block diagram showing details of processingexecuted by the controller 10 in engine control and pump control.

The controller 10 includes two tables 10 a, 10 b for deciding maximumabsorption torques of the hydraulic pump 15 (i.e., maximum pumpabsorption torques) in accordance with the engine revolution speed, aselector 10 c for switching over the maximum pump absorption torquesdecided based on those two tables 10 a, 10 b from one to the otherdepending on which one of the work performance mode and the fuel economymode is selected, and an output unit 10 d for outputting a commandsignal to the torque control solenoid valve 22 so that the maximum pumpabsorption torque selectively switched over by the selector 10 c isobtained.

Further, the controller 10 includes two tables 10 e, 10 f for decidingoutput torques of the engine 1 (i.e., engine output torques) inaccordance with the engine revolution speed, a selector 10 g forswitching over the engine output torques decided based on those twotables 10 e, 10 f from one to the other depending on which one of thework performance mode and the fuel economy mode is selected, and a fuelinjector control unit 10 h for computing a target fuel injection amountand outputting a control signal to the electronic fuel injector 2 sothat the actual engine output torque will not exceed the engine outputtorque selectively switched over by the selector 10 g.

Of the two tables 10 a, 10 b regarding the maximum pump absorptiontorque, the table 10 a is used in the work performance mode and thetable 10 b is used in the fuel economy mode. The tables 10 a, 10 b settherein a pump absorption torque characteristic for the work performancemode and a pump absorption torque characteristic for the fuel economymode, respectively. The pump absorption torque characteristic for thework performance mode is set such that the maximum pump absorptiontorque is constant regardless of the engine revolution speed and theconstant maximum pump absorption torque has, for example, substantiallythe same magnitude TA as that of a conventional setting value of thetorque control regulator. The pump absorption torque characteristic forthe fuel economy mode is set such that the pump absorption torque hassubstantially the same magnitude TA as that of the maximum pumpabsorption torque for the work performance mode in a low revolutionrange and has a magnitude TB slightly smaller than the maximum pumpabsorption torque for the work performance mode in a high revolutionrange.

Of the two tables 10 e, 10 f regarding the engine output torque, thetable 10 e is used in the work performance mode and the table 10 f isused in the fuel economy mode. The tables 10 e, 10 f set therein anengine output characteristic for the work performance mode and an engineoutput characteristic for the fuel economy mode, respectively. FIG. 4comparatively shows the engine output characteristic for the workperformance mode and the engine output characteristic for the fueleconomy mode which are set in the tables 10 e, 10 f, respectively. FIG.4 also shows a specific fuel consumption map. The engine outputcharacteristic for the work performance mode is set so as to provide arelatively large engine output torque in the high revolution range, andthe engine output characteristic for the fuel economy mode is set so asto provide an engine output torque slightly smaller than that for thework performance mode in the high revolution range. An amount by whichthe engine output torque is reduced in the fuel economy mode correspondsto an amount by which the maximum pump absorption torque is reduced. Inother words, the pump absorption torque characteristic for the fueleconomy mode is set such that the maximum pump absorption torque isreduced in an amount corresponding to the amount by which the engineoutput torque is reduced in accordance with the engine outputcharacteristic. Also, since the engine output torque according to thecharacteristic for the fuel economy mode in the high revolution range issmaller than that for the work performance mode, it is positioned on aline representing smaller fuel consumption than that in the workperformance mode.

Each of the two tables 10 a, 10 b receives the revolution speed of theengine 1 detected by the revolution sensor 25 and decides the maximumpump absorption torque corresponding to the received engine revolutionspeed. The selector 10 c receives a signal from the mode select switch11, selects the maximum pump absorption torque decided based on thetable 10 a for the work performance mode when the signal received fromthe mode select switch indicates the work performance mode, and selectsthe maximum pump absorption torque decided based on the table 10 b forthe fuel economy mode when the signal received from the mode selectswitch 11 indicates the fuel economy mode. The maximum pump absorptiontorque selected by the selector 10 c is sent to the output unit 10 d,whereupon the output unit 10 d converts the maximum pump absorptiontorque to a command signal for the torque control solenoid valve 22 andoutputs the command signal.

FIG. 5 shows the relationship between the delivery pressure of thehydraulic pump 15 (i.e., the pump pressure) and the tilting of thehydraulic pump 15 (i.e., the pump tilting) when the torque controlregulator 21 is operated in accordance with the setting value that isvariably controlled by the torque control regulator 22 as describedabove. When the table 10 a for the work performance mode is selected, orwhen the table 10 b for the fuel economy mode is selected and the engine1 is in the low revolution range, the maximum pump absorption torque ofthe hydraulic pump 15 is given as TA. When the table 10 b for the fueleconomy mode is selected and the engine 1 is in the high revolutionrange, the maximum pump absorption torque of the hydraulic pump 15 isgiven as TB. When the pump delivery pressure rises, the torque controlregulator 21 reduces the pump tilting along the characteristic line ofthe maximum pump absorption torque in a responsive manner to control thetilting (displacement) of the hydraulic pump 15 so that the absorptiontorque of the hydraulic pump 15 will not exceed the setting value(maximum pump absorption torque) TA or TB. Also, even at the same pumppressure P1, when the maximum pump absorption torque decreases from TAto TB, the pump tilting is reduced from q1 to q2 and the pump deliveryrate is also reduced correspondingly.

Each of the other two tables 10 e, 10 f receives the revolution speed ofthe engine 1 detected by the revolution sensor 25 and decides the engineoutput torque corresponding to the received engine revolution speed. Theselector 10 g receives a signal from the mode select switch 11, selectsthe engine output torque decided based on the table 10 e for the workperformance mode when the signal received from the mode select switchindicates the work performance mode, and selects the engine outputtorque decided based on the table 10 f for the fuel economy mode whenthe signal received from the mode select switch 11 indicates the fueleconomy mode. The engine output torque selected by the selector 10 g issent to the fuel injector control unit 10 h, which computes the targetfuel injection amount and outputs a control signal to the electronicfuel injector 2 so that the actual engine output torque will not exceedthe selected engine output torque.

FIG. 6 is a functional block diagram showing details of processingexecuted in the fuel injector control unit 10 h.

The fuel injector control unit 10 h has various control functionsexecuted in a revolution speed deviation computing unit 100 a, a fuelinjection amount converting unit 100 b, an integral addition unit 100 c,a maximum fuel injection amount computing unit 100 d, a limit computingunit 100 e, and a primary delay element 100 f.

The revolution speed deviation computing unit 100 a compares the targetengine revolution speed instructed from the travel pedal 8 with theactual engine revolution speed detected by the revolution sensor 25, tothereby compute a revolution speed deviation ΔN. The fuel injectionamount converting unit 100 b multiplies the revolution speed deviationΔN by a gain KF and then executes upper and lower limit processing tocompute an increment ΔFN of the target fuel injection amount. Theintegral addition unit 100 c adds the increment ΔFN to a preceding valueFN2 of a target fuel injection amount FN1 from the primary delay element100 f, thereby computing a new target fuel injection amount FN3.

On the other hand, the engine output torque selected by the selector 10g is sent to the maximum fuel injection amount computing unit 100 d,whereupon the maximum fuel injection amount computing unit 100 dconverts the engine output torque to a fuel injection amount and sendsthe fuel injection amount, as a maximum fuel injection amount FNmax, tothe limit computing unit 100 e. Herein, the engine output torque and thefuel injection amount are substantially in proportional relation, andthe maximum fuel injection amount computing unit 100 d executes theabove conversion based on that relation.

The limit computing unit 100 e multiplies the target fuel injectionamount FN3 by an upper limiter to compute the target fuel injectionamount FN1. A limit value of the upper limiter is variable and set suchthat, as shown in FIG. 7, the limit value of the upper limiter isincreased and decreased as the maximum fuel injection amount FNmaxincreases and decreases.

The target fuel injection amount FN1 obtained by the limit computingunit 100 e is converted to a control current, and the control current isoutputted to the electronic fuel injector 2 for control of the fuelinjection amount. Thus, the fuel injection amount is controlled suchthat the target fuel injection amount FN1 is increased when the actualengine revolution speed is smaller than the target revolution speed(i.e., when the revolution speed deviation ΔN is positive), and thetarget fuel injection amount FN1 is decreased when the actual enginerevolution speed is larger than the target revolution speed (i.e., whenthe revolution speed deviation ΔN is negative). As a result, therevolution speed deviation ΔN becomes 0 and the actual engine revolutionspeed is matched with the target revolution speed. Also, the fuelinjection amount is controlled such that the output torque of the engine1 will not exceed the engine output torque which has been decided basedon the table 10 e or 10 f and selected by the selector 10 g.

In the construction described above, the torque control regulator 21constitutes first pump torque control means for controlling theabsorption torque of the hydraulic pump 15 not to exceed the maximumabsorption torque. The tables 10 a, 10 b, the selector 10 c and theoutput unit 10 d of the controller 10, and the torque control solenoidvalve 22 constitute second pump torque control means for selecting oneof at least two preset pump absorption torque characteristics inresponse to an instruction from the mode select switch 11 andcontrolling the maximum absorption torque of the hydraulic pump 15 inaccordance with the selected pump absorption torque characteristic. Thetables 10 e, 10 f, the selector 10 g, and the fuel injector control unit10 h constitute engine torque control means for selecting one of atleast two engine output torque characteristics in response to theinstruction from the mode select switch 11 and controlling theelectronic fuel injector 2 in accordance with the selected engine outputtorque characteristic, thereby controlling the output torque of theengine 1.

FIG. 8 shows the relationships among the output torque of the engine 1(i.e., the engine output torque), the maximum absorption torque of thehydraulic pump 15 (i.e., the maximum pump absorption torque), and thetransmission torque when the work performance mode is selected. FIG. 9shows the relationships among the engine output torque, the maximum pumpabsorption torque, and the transmission torque when the fuel economymode is selected. In the drawings, A represents the engine output torqueand B represents the maximum pump absorption torque. These torquescorrespond respectively to the engine output torque characteristics setin the tables 10 e, 10 f and the pump absorption torque characteristicsset in the tables 10 a, 10 b. Further, C represents the transmissiontorque. The term “transmission torque” means an input torque of thetransmission 5 when the transmission 5 is driven by the engine 1. Thetransmission torque is increased as the engine revolution speed rises.Also, assuming the definition of a transmission speed ratio=outputrevolution speed of the transmission 5/input revolution speed of thetransmission 5 (=engine revolution speed), the transmission torque isincreased as the speed ratio reduces. The transmission torque shown ineach of FIGS. 8 and 9 represents one at a certain transmission speedratio.

In FIGS. 8 and 9, a torque D available by the transmission 5 (i.e., atravel-available engine output torque D) is smaller than the engineoutput torque by an amount corresponding to the maximum pump absorptiontorque. An intersect M between a characteristic of the travel-availableengine output torque D and a characteristic of the transmission torque Crepresents a matching point, and the engine revolution speed at thematching point M corresponds to the certain transmission speed ratio.

When the work performance mode is selected, the torque decided inaccordance with the engine output torque characteristic set in the table10 e, shown in FIG. 3, is selected as the engine output torque, and thetorque decided in accordance with the pump absorption torquecharacteristic set in the table 10 a, shown in FIG. 3, is selected asthe maximum pump absorption torque. Then, the difference between thoseselected torques is provided as the travel-available engine outputtorque. In this case, the magnitude of the torque decided in accordancewith the pump absorption torque characteristic set in the table 10 a issubstantially the same as that conventionally set. Therefore, thedelivery rate of the hydraulic pump 15 is relatively large andsufficient work performance can be ensured. Further, since the engineoutput torque characteristic set in the table 10 e provides a relativelylarge torque in the high revolution range, the characteristic of thetravel-available engine output torque D also provides a relatively largetorque in the high revolution range, and hence a sufficient travel forcecan be obtained at the matching point M.

When the fuel economy mode is selected, the torque decided in accordancewith the engine output torque characteristic set in the table 10 f,shown in FIG. 3, is selected as the engine output torque, and the torquedecided in accordance with the pump absorption torque characteristic setin the table 10 b, shown in FIG. 3, is selected as the maximum pumpabsorption torque. Then, the difference between those selected torquesis provided as the travel-available engine output torque. In this case,the engine output torque characteristic set in the table 10 f providesthe torque having a magnitude slightly smaller than that in the workperformance mode in the high revolution range. Correspondingly, the pumpabsorption torque characteristic set in the table 10 b also provides thetorque having a magnitude slightly smaller than that in the workperformance mode in the high revolution range. Therefore, the deliveryrate of the hydraulic pump 15 is slightly reduced and so is the workperformance. However, since the magnitude of the travel-available enginetorque in the high revolution range is substantially the same as thatwhen the work performance mode is selected, the travel force is heldsubstantially the same as that when the work performance mode isselected, whereby a sufficient travel force can be obtained.

Further, the engine output torque is slightly reduced in the highrevolution range. As shown in FIG. 4, therefore, the engine 1 can beoperated in an area of the specific fuel consumption map where a smallerfuel consumption rate is obtained, and fuel economy can be improved.

According to this embodiment, as described above, when the workperformance mode is selected by the mode select switch 11, the torquedecided in accordance with the engine output torque characteristic setin the table 10 e and adapted for higher work performance is selected,and therefore the work performance can be increased. When the fueleconomy mode is selected, the torque decided in accordance with theengine output torque characteristic set in the table 10 f and adaptedfor fuel economy is selected, and therefore the fuel economy effect canbe obtained. Also, when the fuel economy mode is selected, the torquedecided in accordance with the pump absorption torque characteristic setin the table 10 b and having a relatively small torque in the highrevolution range is selected, and therefore the torque decided inaccordance with the engine torque characteristic for traveling in thehigh revolution range is not reduced. As a result, a large travel forcecan be maintained and good workability can be held.

A second embodiment of the present invention will be described belowwith reference to FIGS. 10 and 11. In these drawings, identicalcomponents to those shown in FIGS. 3 and 6 are denoted by the samesymbols.

FIG. 10 is a functional block diagram showing details of processingexecuted by a controller in engine control and pump control according tothis embodiment. FIG. 10 corresponds to FIG. 3 regarding the firstembodiment. Also, FIG. 11 is a functional block diagram showing detailsof processing executed in a fuel injector control unit. FIG. 11corresponds to FIG. 6 regarding the first embodiment.

In this second embodiment, two tables 10Ae, 10Af for the engine control,shown in FIG. 10, set therein characteristics of the fuel injectionamounts instead of the engine output torques, and directly decide thefuel injection amounts in accordance with the engine revolution speed.In this case, the term “fuel injection amount” means the fuel injectionamount per engine revolution, and the characteristics of the fuelinjection amounts are decided in accordance with the engine outputtorque characteristics set in the tables 10 e, 10 f in the firstembodiment. Stated another way, the tables 10Ae, 10Af set therein thefuel injection amount characteristic for the work performance mode andthe fuel injection amount characteristic for the fuel economy mode,respectively, and those characteristics are ones capable of realizingthe engine output torque characteristic for the work performance modeand the engine output torque characteristic for the fuel economy modewhich are set in the tables 10 e, 10 f, respectively.

As a result, in a fuel injector control unit 10Ah, the maximum fuelinjection amount computing unit 100 d is no longer required, and thefuel injection amount selected by the selector 10 g is directly inputtedas the maximum fuel injection amount FNmax to the limit computing unit100 e.

In the construction described above, the tables 10 a, 10 b, the selector10 c and the output unit 10 d of the controller 10, and the torquecontrol solenoid valve 22 (see FIG. 1) constitute second pump torquecontrol means for selecting one of at least two preset pump absorptiontorque characteristics in response to an instruction from the modeselect switch 11 and controlling the maximum absorption torque of thehydraulic pump 15 in accordance with the selected pump absorption torquecharacteristic. The tables 10Ae, 10Af, the selector 10 g, and the fuelinjector control unit 10Ah constitute engine torque control means forselecting one of at least two preset engine output torquecharacteristics in response to the instruction from the mode selectswitch 11 and controlling the electronic fuel injector 2 in accordancewith the selected engine output torque characteristic, therebycontrolling the output torque of the engine 1.

This embodiment thus constructed can also provide similar advantages tothose obtained with the first embodiment.

In addition, according to this embodiment, since the fuel injectionamount per engine revolution is directly determined corresponding to theengine revolution speed, more accurate torque control can be performedat each engine revolution speed.

1. A control system for a working vehicle comprising an engine, a travelpedal for instructing a target revolution speed of said engine, a fuelinjector for controlling a fuel injection amount depending on the targetrevolution speed of the engine thereby to control an output torque andrevolution speed of said engine, a transmission for traveling includinga torque converter which is driven by said engine, a variabledisplacement hydraulic pump driven by said engine, and a hydraulicactuator driven by a hydraulic fluid delivered from said hydraulic pump,and first pump torque control means for controlling an absorption torqueof said hydraulic pump not to exceed a maximum absorption torque,wherein said control system comprises: switching-over means; enginetorque control means for selecting one of at least two preset engineoutput characteristics with respect to an engine revolution speed inresponse to an instruction from said switching-over means, determining amaximum fuel injection amount corresponding to the engine revolutionspeed at the current time in accordance with the selected engine outputcharacteristic, and controlling said fuel injector such that the fuelinjection amount controlled depending on the target revolution speed ofthe engine does not exceed said maximum fuel injection amount, therebycontrolling the output torque of said engine; and second pump torquecontrol means for selecting one of at least two preset pump absorptiontorque characteristics with respect to an engine revolution speed inresponse to the instruction from said switching-over means anddetermining a maximum absorption torque corresponding to the enginerevolution speed at the current time in accordance with the selectedpump absorption torque characteristic, thereby controlling the maximumabsorption torque of said hydraulic pump; and said switching-over meansis a switch for instructing one of a work performance mode and a fueleconomy mode; said engine torque control means selects the output torquecharacteristic providing, in the fuel economy mode, a slightly smallerengine output torque in a relatively high range of the engine revolutionspeed than that in the work performance mode; and said second pumptorque control means selects the pump absorption torque characteristicproviding, in the fuel economy mode, a slightly smaller maximum pumpabsorption torque in the relatively high range of the engine revolutionspeed than that in the work performance mode corresponding to areduction of the engine output torque made by said engine torque controlmeans.
 2. The control system for the working vehicle according to claim1, wherein said engine torque control means sets, as the engine outputcharacteristic, an engine output torque characteristic with respect tothe engine revolution speed and determines an engine output torquecorresponding to the engine revolution speed at the current time inaccordance with the selected engine output torque characteristic, andthen converts the determined engine output torque into said maximum fuelinjection amount.
 3. The control system for the working vehicleaccording to claim 1, wherein said engine torque control means sets, asthe engine output characteristic, a fuel injection amount characteristicwith respect to the engine revolution speed and determines a fuelinjection amount corresponding to the engine revolution speed at thecurrent time, and then uses the determined fuel injection amount as saidmaximum fuel injection amount.